2
https://raw.githubusercontent.com/njcodernoob/codility-java-solutions/master/DistinctSolution2.java
package com.challenges;

/*
 * 
 * Write a function

class Solution { public int solution(int[] A); }

that, given an array A consisting of N integers, returns the number of distinct values in array A.

For example, given array A consisting of six elements such that:

 A[0] = 2    A[1] = 1    A[2] = 1
 A[3] = 2    A[4] = 3    A[5] = 1
the function should return 3, because there are 3 distinct values appearing in array A, namely 1, 2 and 3.

Write an efficient algorithm for the following assumptions:

N is an integer within the range [0..100,000];
each element of array A is an integer within the range [−1,000,000..1,000,000].
 * 
 */

public class DistinctSolution2 {

	public int solution(int[] a) {
		// write your code in Java SE 8
        
        int ans = 0;
        
        boolean [] positives = new boolean[1000001];
        boolean [] negatives = new boolean[1000001];
        
        for (int i = 0; i < a.length; i++) {
            if (a[i] < 0) {
                negatives[-a[i]] = true;
            } else {
                positives[a[i]] = true;
            }
        }
        
        for (int i = 0; i <= 1000000; i++) {
            if (positives[i] == true) ans++;
            if (negatives[i] == true) ans++;
        }
        
        return ans;
        
    }

}
